class Zip::ExtraField::Zip64

def pack_for_c_dir
  # central directory entries contain only fields that didn't fit in the main entry part
  packed = ''.force_encoding('BINARY')
  packed << [@original_size].pack('Q<') if @original_size
  packed << [@compressed_size].pack('Q<') if @compressed_size
  packed << [@relative_header_offset].pack('Q<') if @relative_header_offset
  packed << [@disk_start_number].pack('V') if @disk_start_number
  packed
end